The present invention relates to a process for upgrading feedstocks containing paraffins. This process involves isomerization and/or disproportionation over a catalyst comprising MCM-36. Paraffin isomerization may involve skeletal rearrangement of low octane linear paraffins and only slightly branched paraffins to higher octane, more highly branched paraffins. Paraffin disproportionation involves converting paraffins to other paraffins containing at least one more and at least one less carbon fragment per molecule. In the present process, paraffins produced by disproportionation tend to have a large degree of branching.
A unit process which is frequently encountered in petroleum refining is paraffin isomerization. Paraffin isomerization of linear (straight chain) paraffins produces branched chain paraffins. In such a process, as conventionally operated, low molecular weight C.sub.4 -C.sub.6 paraffins are converted to iso-paraffins in the presence of an acidic catalyst such as chlorided alumina. Recently, C.sub.6 +, preferably C.sub.10 + n-paraffins, have been isomerized, in the presence of large pore size zeolites to produce branched chain paraffins by skeletal rearrangement. The latter process can find application in dewaxing.
Isomerization is one of several reactions which occur in reforming of naphthas. Reforming of naphthas is undertaken to upgrade a low octane naphtha to a higher octane effluent. One of the octane enhancing reactions which occurs during reforming is the isomerization of n-paraffins to isoparaffins. Under the process conditions of reforming, other reactions which occur are aromatization (or dehydrocyclization), dehydrogenation, with some cracking.
Paraffin isomerization catalysts may also be employed as ring opening catalysts for removal of cyclic aromatic precursors from reformer feedstocks. For example, cyclohexane, a precursor to benzene, is rearranged over commercial paraffin isomerization catalysts to a mixture of branched paraffins. Branched paraffins are only partly aromatized in reforming whereas cyclohexane is completely converted to aromatics, mostly benzene. Application of paraffin isomerization catalysts for ring opening aromatics precursors will no doubt become more important as environmental regulations limiting aromatics in gasoline become more stringent.
U.S. Pat. No. 5,107,054 describes the use of a zeolite, designated MCM-22, to catalyze the isomerization of certain paraffins, such as those included in a low octane, light straight run naphtha.
Zeolite catalyzed paraffin disproportionation reactions are described in a number of U.S. Patents. U.S. Pat. No. 3,914,331 describes the use of ZSM-4 to catalyze the disproportionation of certain paraffins including pentane and hexane.
U.S. Pat. No. 3,953,537 describes the use of certain large pore size zeolites, such as synthetic faujasite, to catalyze the disproportionation of certain paraffins, such as propane, butane and pentane.
U.S. Pat. No. 4,686,316 describes the use of certain medium pore size zeolites, such as ZSM-5, to catalyze the conversion of propane to a product comprising isobutane.
U.S. Pat. No. 4,929,793 describes the use of certain medium pore size zeolites, such as ZSM-5, to catalyze the disproportionation of certain paraffins, such as those included in a C.sub.5 to C.sub.9 UDEX raffinate.
U.S. Pat. No. 5,171,912 describes the use of certain medium pore size zeolites, such as ZSM-5 and MCM-22, to catalyze the disproportionation of propane and butane.